Hotfix: Correctly set overwrite option when specified

[DavidHuber-NOAA]

Description

This specifies a correct option for the overwrite option in setup_expt.py when called with the --overwrite flag. As-is, the EXPDIR and COMROOT directories are not actually deleted when --overwrite is specified.

This also removes an unused module (warnings) and method (to_timedelta) from setup_expt.py.

Type of change

• Bug fix (fixes something broken)

Change characteristics

• Is this a breaking change (a change in existing functionality)? NO
• Does this change require a documentation update? NO
• Does this change require an update to any of the following submodules? NO

How has this been tested?

Ran setup_expt.py with --overwrite and verified the EXPDIR and COMROOT were actually deleted before repopulating.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added

[KateFriedman-NOAA]

Looks good, thanks @DavidHuber-NOAA !